Smallest main I had on hand was a 165. I don't work on 450s, so this is new to me and slowly getting a collection of tuning jets. It was very rich, didn't have the A/F meter on at the time. When we opened the air box door we got 3 HP and it reved another 2,000 RPMS. Im guessing MJ should be around 160-165 depending on how much air I can get in there. I'm going to work on the air box snorkel and a small door vent mod to get more air in. It's a work in progress... Learning as I go. Pete, are you still running the header pipe with the CAT inside?